This slide shows a remarkable increase in the number of eosinophilic granulocytes. The bulk of the eosinophils are dysplastic, showing a hypersegmented nucleus and/or hypogranulation. A single eosinophil is even completely empty. This myeloproliferative form of the hypereosinophilic syndrome (M-HES, also called chronic eosinophilic leukemia) in this patient was caused by fusion of the genes FIPIL1 and PDGFRA.